1.2 Evolution of Scientific Ideas (Paradigms)

Introduction

Science does not stand still. The way scientists explain nature changes over time as new evidence appears. Old ideas are replaced by better ones. These shifts in thinking are called changes in scientific paradigms.

This section explains what a scientific paradigm is and gives three important examples from chemistry:

• The Phlogiston Theory
• Historical Models of the Atom
• The Periodic Table

Definition

Scientific Paradigm: A scientific paradigm is a set of ideas, methods, and rules that guide scientists in their research. It helps scientists understand the natural world and explain their discoveries. It gives scientists a consistent way to study and share knowledge.

In simple words: A paradigm is the "accepted way of thinking" during a particular time. It is the framework that scientists use to explain how nature works.

Main Idea

• A paradigm is the dominant framework of ideas in a science at a given time.
• It guides what scientists study, how they study it, and how they interpret results.
• When new evidence challenges an existing paradigm, it may be replaced by a better one.
• This replacement is called a paradigm shift.

Core Concept

A paradigm is not just one theory. It is a whole way of thinking that includes:

• accepted theories
• standard methods
• common assumptions
• shared language and terminology

When scientists work within a paradigm, they are solving puzzles using the accepted rules. When too many puzzles cannot be solved, the paradigm is challenged and may be replaced.

Detailed Explanation

What is a Scientific Paradigm?

A scientific paradigm is a set of ideas, methods, and rules that guide scientists in their research.

What a paradigm does:

• helps scientists understand the natural world
• helps explain discoveries
• gives a consistent way to study and share knowledge
• guides research and development
• helps scientists understand the behaviour of chemicals and their interactions

What happens when a paradigm is challenged:

• new evidence may not fit the old paradigm
• scientists debate and test the new evidence
• if the evidence is strong enough, the old paradigm is replaced by a better one

Examples of paradigms in chemistry:

• the belief that materials burn because they contain "phlogiston" (18th century)
• historical models of the atom (plum-pudding, Rutherford, Bohr, quantum)
• the periodic table and the belief in "periodicity" of atoms based on electron arrangements

1. The Phlogiston Theory

What it was: In the 1700s, scientists believed in the phlogiston theory to explain burning (combustion) and rusting.

The idea: According to this theory, materials that could burn contained a substance called "phlogiston". When the material burned, phlogiston was released into the air.

Example: When metals rusted, people thought they absorbed "deflogisticated air" (air that had lost its phlogiston).

Why it was accepted: It seemed to explain why things burn and why metals change when heated.

How it was replaced: Antoine Lavoisier proved that combustion happens because of oxygen combining with substances, not because of phlogiston. His work introduced a new way of thinking about chemical reactions, replacing the phlogiston theory with the modern concepts of oxidation and reduction.

Why this is a paradigm shift: The old framework (phlogiston) was replaced by a new framework (oxygen-based combustion). This changed how chemists understood burning, rusting, and chemical reactions in general.

2. Historical Models of the Atom

Scientists have changed their ideas about what atoms look like as they learned more through experiments.

The Plum Pudding Model (1904):

• Proposed by J.J. Thomson.
• Suggested that atoms are like a "pudding" with negatively charged electrons (the "plums") scattered in a positively charged "soup."

Rutherford's Model (1911):

- Ernest Rutherford's gold foil experiment showed that atoms have a small, dense, positively charged centre called a nucleus, with electrons orbiting around it.

Bohr's Model and Quantum Model:

- Later, scientists improved Rutherford's model by adding ideas about energy levels (Bohr's model) and quantum mechanics, which is the current way we understand atoms.

Why these changes happened: New experiments provided better evidence. Each new model explained the evidence better than the previous one.

Why this is a paradigm shift: Each model represented a different framework for understanding the atom. The change from plum pudding to Rutherford to Bohr to quantum mechanics is a series of paradigm shifts.

3. The Periodic Table

Who created it: Dmitri Mendeleev created the periodic table in 1869.

How he organized it: He organized elements based on their atomic masses and properties.

Why it was powerful: His table predicted the existence of elements that had not been discovered yet. When those elements were later discovered, their properties matched Mendeleev's predictions.

Why this is a paradigm: The periodic table and the belief in the "periodicity" of atoms based on the arrangements of their electrons is a paradigm. It provides a framework for understanding the properties of materials and for developing new materials with specific properties.

How it guides research: The periodic table guides research and development in chemistry. It helps scientists better understand the behaviour of chemicals and their interactions.

Intermediate Level

A scientific paradigm includes:

• accepted theories
• standard methods
• common assumptions
• shared language

It guides what scientists study and how they interpret results.

Paradigm shifts in chemistry:

When new evidence challenges an existing paradigm, it may be replaced with a better one.

Important Points

• - A scientific paradigm is a set of ideas, methods, and rules that guide scientists.
• - Paradigms give scientists a consistent way to study and share knowledge.
• - When new evidence challenges a paradigm, it may be replaced by a better one.
• - Phlogiston theory was replaced by Lavoisier's oxygen theory of combustion.
• - Atomic models changed from plum pudding → Rutherford → Bohr → quantum.
• - Mendeleev's periodic table organized elements and predicted new ones.
• - The periodic table is a paradigm that guides research in chemistry.

Remember

• - Paradigm = accepted framework of ideas in science.
• - Paradigm shift = replacement of an old paradigm by a new one.
• - Phlogiston → Oxygen (Lavoisier).
• - Plum pudding → Rutherford → Bohr → Quantum.
• - Mendeleev's periodic table = paradigm based on periodicity.
• - Paradigms guide research and development in chemistry.

Common Mistakes

Quick Revision

A scientific paradigm is a set of ideas, methods, and rules that guide scientists in their research. It helps scientists understand nature and share knowledge. When new evidence challenges a paradigm, it may be replaced by a better one.

Three examples:

• Phlogiston theory → replaced by Lavoisier's oxygen theory of combustion.
• Atomic models: plum pudding (Thomson) → Rutherford → Bohr → quantum mechanical.
• Periodic table (Mendeleev, 1869): organized elements by atomic mass and properties; predicted new elements.

Paradigms guide research and development in chemistry.

60-Second Revision

• Paradigm = accepted framework of ideas, methods, and rules in science.
• Paradigm shift = old paradigm replaced by a better one when new evidence appears.
• Phlogiston theory → Lavoisier's oxygen theory of combustion.
• Atom models: plum pudding → Rutherford → Bohr → quantum.
• Mendeleev's periodic table (1869) = paradigm based on periodicity; predicted undiscovered elements.
• ⚠️ Warning: a paradigm is not just one theory — it is a whole way of thinking.